In recent years, from the viewpoint of the protection of the global environment, there is an attempt to reduce the discharge amount of exhaust gas or the amount of fuel consumption of a vehicle, and to make the vehicle travel (hereinafter, referred to as “ecological”, “ecological traveling”, or “ecological driving”) contributing to the protection of the environment. For example, Patent Literature 1 describes a navigation system in which the current position and the traveling locus of a vehicle are successively displayed on a display unit, and the traveling performance (vehicle speed or mileage) of the vehicle is displayed on the traveling locus.
In this navigation system, the display color or display line of the traveling locus changes depending on the traveling performance. In this navigation system, for example, the traveling locus is displayed green when the vehicle speed is equal to or lower than 20 km/h, blue when the vehicle speed is 20 km/h to 40 km/h, black when the vehicle speed is 40 km/h to 80 km/h, and red when the vehicle speed is equal to or higher than 80 km/h, thereby allowing a driver to intuitively perceive the traveling performance.